1. Field of the Invention
The present invention relates to a color image forming apparatus and, more particularly, to an apparatus for receiving at least one of the coded character information, coded figure information, and bit image information from a host apparatus and forming a color image.
2. Related Background Art
Hitherto, a color graphic display has mainly been used as an apparatus for receiving PDL (Page Description Language) data including color information as input data and forming an image on the basis of the input data. The PDL is a language to describe output data of a page layout software system and describes an objective image by combining an image description of character code, an image description of figure code, and an image description of bit data which are handled by the page layout software as shown in FIG. 5A. The graphic display which receives the PDL data as input data generally has three bit map memories, for red (R), green (G), and blue (B). The image data are respectively indicated by the image description of character code, image description of figure code, and image description of bit data are developed in the respective bit map memories in accordance with the color information in the PDL data and displayed. Further, in many cases, a color image which is used in a computer is ordinarily dissolved into three color components of R, G, and B and provided. Therefore, the PDL including the color information generally handles the color information as three color components of R, G, and B.
However, in ordinary color printers, an image is formed by the primary color components, for instance, cyan, magenta, and yellow of the subtractive color mixing system which mixes color materials, as red, green, and blue as the primary color components of the additive color mixing system which are used in the color graphic display (for instance, CRT) cannot be used and must be converted.
Further, if an image forming method for use in the above display is applied to a color printer of a high resolution and multi-gradations, the memory capacity increases greatly because of the following two reasons.
1) In the case of the display, it is sufficient to provide three bit map memories for R, G, and B. However, to obtain a high quality image such as a beautiful black character or the like by the color printer, the black component is necessary in addition to the color components of cyan, magenta, and yellow. Further, to obtain a high gradation image, data of six to eight bits must be provided for each color component, so that the memory capacity which is necessary for every pixel increases.
2) The resolution of the high resolution printer is set to 400 dpi (dots per inch) and the number of pixels constructing an image is larger than that in the case of the graphic display whose resolution is about 70 dpi.
Therefore, in the color printer in which, for instance, the resolution is set to 400 dpi, four color materials of yellow, magenta, cyan, and black are used, and the data regarding each color component consists of eight bits, a memory having the memory capacity of about 64 Mbytes is needed to construct the bit map memory of the A4 size. The necessity of such a large amount of memory results in one problem in development of a color image forming apparatus (for instance, color printer) which receives the PDL data as input data.
On the other hand, nothing has been proposed yet with respect to a point that the PDL data for the graphic display is applied to the color printer which forms an image by color components other than R, G, and B. If such PDL data is simply applied to the color printer, the following drawbacks occur.
Since the positions in color space of the color components differ in accordance with the color materials in dependence on the color printer, when the input color component data of R, G, and B are inverted and the component data of C, M, and Y as the complementary colors are merely formed, the correct color is not formed.